Adjust string entry on mission screens to allow non-alphanumeric on SDL

Issue #91 (needs further testing on Windows and Mac platforms)
Fix for issue #95

Force run loop evaluation on Windows while download progresses.
More docking fixes

- Fly away from destination will now turn if pointing right at the coordinates
- if max_cos is increased, min_d is decreased to allow course corrections to be carried out
- minimum approach to coordinates speed reduced for docking
Precautionary fix

Ships with high speed/roll/pitch might need even more slowdown
Update changelog